<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  
  <script>


   for(;;){

    let userName=prompt('请输入用户名')
    let keysword=Number(prompt('请输入密码'))

    if(userName==='admin'&&keysword===123456){
      alert('登入成功')
      break
    }
   }

   console.log(typeof(admin));//结果为underfind
   // 用户输入的是字符串类型，只有给admin加上上引号变成字符串 ===两边才能相等

  </script>
</body>
</html>